Nematodes are elongated symmetrical roundworms that constitute one of the largest and most successful phyla in the animal kingdom. Many nematode species are free-living and feed on bacteria, whereas others have evolved into pests or parasites of plants and animals, including humans.
Nematode pests of plants are responsible for many billions of dollars in economic losses annually. Nematode plant pests feed on stems, buds, leaves and, in particular, on roots of more than 2,000 vegetables, fruits, and ornamental plants, causing an estimated $100-125 billion crop loss worldwide. Nematodes are present throughout the United States (US), but are mostly a problem in warm, humid areas of the south and west, as well as in sandy soils. The most economically damaging plant nematode pest genera belong to the family Heterderidae of the order Tylenchida, and include the cyst nematodes [genera Heterodera and Globodera, e.g., soybean cyst nematode (Heterodera glycines, SCN) and potato cyst nematodes (G. pallida and G. rostochiensis)], and the root-knot nematodes (genus Meloidogyne).
Root-knot nematodes infest thousands of different plant species including vegetables, fruits, and row crops. Cyst nematodes are known to infest tobacco, cereals, sugar beets, potato, rice, corn, soybeans and many other crops. Heterodera schachtii (BCN) principally attacks sugar beets, and Heterodera avenae is a pest of cereals. Heterodera zeae feeds on corn, and Globodera rostochiensis and G. pallida feed on potatoes. The soybean cyst nematode (SCN) is present in every soybean-producing state in the US, and causes total soybean yield losses estimated to be nearly $1 billion per year. Once SCN is present in a field, it cannot feasibly be eradicated using known methods. Although soybean is the major economic crop attacked by SCN, SCN attacks at least fifty other hosts, including field crops, vegetables, ornamentals, and weeds.
Signs of nematode damage include stunting and yellowing of leaves, as well as wilting of the plants during hot periods. However, nematodes can cause significant yield loss without obvious above-ground symptoms. For example, an infestation of SCN in a plant can result in dwarfed or stunted roots, decrease the number of nitrogen-fixing nodules on the roots, and/or make the roots more susceptible to attack by other soil-borne plant pests or pathogens.
In contrast to many viral and bacterial pathogens, little is known about the molecular basis of the nematode-plant interaction, limiting the available approaches useful in controlling nematodes. Chemicals useful in controlling nematode plant pests include organophosphates and carbamates, the oldest extant class of nematicides, which target acetylcholinesterase. Imidazole derivatives such as benzimidazole exert their nematicidal effects by binding tubulin. Levamisole acts as an agonist on the nicotinic acetylcholine receptor, and avermectins act as irreversible agonists at glutamate-gated chloride channels. Unfortunately, there are certain debilitating nematode infestations which are difficult, if not impossible, to eradicate with existing control measures.
Nematode resistant germplasm and transgenic plants have also been considered as alternatives or complements to chemical control measures. Different varieties of soybean vary in their sensitivity or resistance to root knot nematode infestation. Therefore, one effective control measure for nematode infestation is planting nematode resistant soybean varieties. Accordingly, varietal selection is an important tool for management of nematode infestation. However, currently, determining whether a soybean cultivar might be nematode resistant typically involves testing the phenotype of each cultivar in the field or greenhouse.
Thus, the present invention overcomes shortcomings in the art by providing markers associated with resistance to root knot nematode, thereby allowing the characterization of soybean cultivars for such resistance by molecular analysis rather than phenotypic analysis.